Integrated circuit (IC) chips, such as microprocessors or micro-computers have enabled a dramatic reduction in the space requirements for electronic circuitry. The typical IC chip is a rectangular structure, having an outer portion formed from an insulating material Embedded centrally within insulating material is a small, but complicated, array of circuitry such as the microprocessor or micro-computer. Electrically conductive leads, also embedded in the insulating material extend from the microprocessor to downwardly extending pins that typically are mounted on opposed side edges of the chip. The pins provide the connection between the microprocessor and other components of the device in which the chip is used. In most instances, this connection is made by mounting the chip on a printed circuit board having conductive leads extending to other electrical components of the device.
The flow of electricity generates heat directly proportional to the amount of electric current and inversely proportional to the size of the electrically conductive area. Since the microprocessor, micro-computer or other complex circuitry of the IC chip accommodates a relatively large amount of electrical current flow within an extremely small area, the chips generate a substantial amount of heat. This heat can affect the efficiency and operability of the IC chip, and thus of the entire device within which the chip is used. The effect of the heat generated by IC chips is exacerbated by the close spacing of chips and other components on printed circuit boards, and the close spacing of printed circuit boards within electrical devices.
Heat dissipators or heat sinks are used to offset the heat generated by IC chips. The heat dissipators or sinks conduct heat away from the chip, thereby maintaining the operating temperature of the chip at an acceptable level. The heat conducted from the chip then is radiated to the surrounding air and dissipated by convection. Heat dissipators generally are utilized in conjunction with all but the smallest integrated circuit chips, and are virtually mandatory in the larger chips housing microprocessors or micro-computers which have a vast amount of circuitry in a small area.
The most commonly used prior art heat dissipator consists of a unitary member of heat conductive material that is adhesively mounted to the top surface of the chip. These prior art dissipators, although functional, have disadvantages. One disadvantage relates to the structure of the chip itself. Specifically, the circuitry in the chip is located such that most of the generated heat is directed through the bottom surface of the chip. For example, it is estimated that in the typical IC chip between 60% and 66% of the heat generated by the chip passes through its bottom surface. As a result, the single member heat dissipator adhesively mounted on the top of the chip is able to conductively dissipate only a small part of the heat generated by the chip. Thus, the single member prior art heat dissipator described above has only limited effectiveness for dissipating the heat generated by IC chips. Another disadvantage is that the adhesive attachment of the dissipator to the chip precludes reuse of the dissipator when a chip is replaced. Additionally, the adhesives add to the time and cost of manufacture.
Other prior art heat dissipators have been developed which consist of separate top and bottom members to contact respectively the top and bottom surfaces of the chip. By providing direct contact to both opposed surfaces of the chip, these two member heat dissipators more efficiently reduce operating temperatures.
Prior art two member heat dissipators have been developed in many structural forms. For example, in certain prior art heat dissipators, both the top and bottom members are adhesively affixed to the respective top and bottom surfaces of the chip. Although this arrangement dissipates heat, it has several disadvantages. Specifically, the adhesive attachment of the dissipator to the chip adds to the time and cost required to assemble the electrical apparatus. Additionally, the adhesive attachments of the dissipator to the chips are permanent. Consequently, new top and bottom members of the dissipator must be provided if the chip is changed.
Two member heat dissipators have been developed which rely on screws, bolts, rivets or other separate mechanical connectors instead of the adhesives described above. The members of these prior art dissipators can be affixed mechanically to either one another or to adjacent portions of the printed circuit board. Although these dissipators can be reused, the connecting structures add substantially to the cost associated with manufacture and assembly.
In many prior art two member heat dissipators, the bottom member contributes only minimally to the heat dissipation function. For example, bottom members often are small and narrow providing for little conduction or radiation of heat away from the IC chip. In other prior art two member heat dissipators, attempts are made to enhance the radiation from the chip by providing a plurality of outwardly extending vanes or fins on the top member. These fins typically extend well beyond the plan dimension of the chip, thereby increasing the space requirements within the electrical device.
In still another prior art two member heat dissipator, as shown in U.S. Pat. No. 4,235,285, a pair of inwardly and outwardly rolled clasp members are used to inter-engage the top and bottom members. The dissipator shown in U.S. Pat. No. 4,235,285 also has several disadvantages. First, vibrations in the electrical device can cause the bottom member to move relative to the top member and the chip, thereby creating the risk of contact with the pins and a resultant short circuiting. Second, the dissipator taught by U.S. Pat. No. 4,235,285 extends substantially beyond the plan dimensions of the chip in order to attain the proper heat dissipation. Specifically, the alternate embodiments shown in U.S. Pat. No. 4,235,285 either include outwardly extending radiating fins or large looping clasps that perform both a connecting and a heat radiating function. These added space requirements of the heat dissipator often control the overall size of the electrical device in which it is used. Third, the various embodiments shown in U.S. Pat. No. 4,235,285 do not effectively enable the conduction and then radiation of heat upward and away from the bottom surface of the IC chip. More particularly, the heat either is radiated initially through conducting planes that are substantially parallel to the planes of the chip and the circuit board, or the heat from the bottom surface must be radiated through the top contact plate to reach the fins. Thus, these embodiments do not directly radiate the substantial heat generated by the bottom surface of the chip upward and away from the chip and the circuit board. Fourth, the rolled clasp connection between the top and bottom members provides for poor heat conduction between those two members. As a result the effectiveness of the top member in radiating heat generated from the bottom surface is reduced. Fifth, the devices require awkward and difficult manipulation to be effectively mounted. Finally, the complex arrangement of rolled clasps and interengaging loops contributes to the manufacturing cost.
Accordingly, it is an object of the subject invention to provide a heat dissipator for use with IC chips that effectively dissipates heat from both the top and bottom surfaces of the chip.
It is another object of the subject invention to provide a heat dissipator for use with IC chips that does not require adhesive mounting on the chip.
It is a further object of the subject invention to provide a heat dissipator for use with integrated circuit chips that does not require ancillary mounting devices.
It is still another object of the subject invention to provide a heat dissipator for use with IC chips that can be easily mounted on the chip.
It is still a further object of the subject invention to provide a heat dissipator for use with IC chips that can be easily removed from the chip and subsequently reused.
It is still an additional object of the subject invention to provide a heat dissipator for use with IC chips that does not extend beyond the plan dimensions of the chips.
It is yet another object of the subject invention to provide a heat dissipator for use with IC chips that can be securely mounted on the chips thereby avoiding potential shorting against the electrically conductive members of the chip.